Prime Minister David Cameron has hit out at allegations he carried out an obscene act with a dead pig while at university.

Mr Cameron said people would “see straight through” the motives behind the book which contains a series of damaging allegations including stories about him smoking cannabis at Oxford University and cocaine allegedly being in circulation at a party hosted by Mr Cameron.

Lord Ashcroft – who gave the Conservatives £8 million while the party was in opposition – said he decided to write the book when Mr Cameron failed to reward him with a sufficiently senior job in government when he came to power in 2010.

The book, co-written with the journalist Isabel Oakeshott and serialised in the Daily Mail, has made international headlines with its allegations about Cameron’s lifestyle while a student at Oxford University.